如何制作一个函数来判断 python 中两个列表是否相等

Question

这个问题真的很烦人，因为它是针对 class 的，而且我们的代码有很多限制。

objective是做一个函数，看两个列表（随机排序）是否有相同的元素。因此，如果 a=[2,5,4] 和 b=[4,2,5] a==b 将是 true。现在的限制是我们不能使用除 len() 之外的任何内置函数。所以我不能使用 set() 之类的东西。我也不允许编辑列表，所以我无法检查项目是否在两个列表中，如果它们在两个列表中，我就删除它们，直到它为空。

由于所有这些限制，我运行没有想法。请帮忙。

Answer 1

显然最好的解决方案是使用 set()，但您受到限制。这是一种没有任何 "built-in functions":

的方法

def equal_lists(l1, l2):
    for i in l1:
        if not i in l2:
            return False
    for i in l2:
        if not i in l1:
            return False
    return True

编辑如果你想 "account for two lists with all the same elements but different numbers of each":

def occur(it):
    d = {}
    for i in it:
        try:
            d[i] += 1
        except KeyError:
            d[i] = 1
    return d

occur(a) == occur(b)

Answer 2

是否允许递归？这样，您就不必修改现有列表。显然，效率不是很高，但考虑到您的要求，这应该不是真正的问题...

def are_items_equal(a, b):
    # First the guard clause: if the first list is empty,
    # return True if the second list is empty too, False otherwise
    if not a:
        return not b

    # There is now at least 1 item in list a
    # Perform a linear search in the b list to find a[0]
    # (could have used a "for" loop, but I assumed here this was
    # forbidden too)
    ib = 0;
    while ib < len(b):
        if a[0] == b[ib]:
            # At this point, we know that at index `ib` in list `b`
            # there is the same item as in `a[0]`
            # Both list match if the "rest" of those two lists match too
            # Check that by performing a recursive call to are_items_equal
            # (discarding the pair matched at this step)
            return are_items_equal(a[1:], b[:ib]+b[ib+1:])
        ib += 1

    # You only reach this point when `a[0]` was not found
    # in the `b` list.
    return False

测试：

test_case = (
    ([2,5,4], [4,2,5]),
    ([2, 2, 5, 4], [4, 5, 2, 5]),
    ([2,2,5,4], [4,2,5]),
    ([2,2,5,4],[4,2,5,2]),
)

for a,b in test_case:
    print(are_items_equal(a, b), a, b)

制作中：

True [2, 5, 4] [4, 2, 5]
False [2, 2, 5, 4] [4, 5, 2, 5]
False [2, 2, 5, 4] [4, 2, 5]
True [2, 2, 5, 4] [4, 2, 5, 2]

如何制作一个函数来判断 python 中两个列表是否相等

how to make a function which tells if two lists are equivalent in python

python

function

equivalence